1. Field of the Invention
The present invention relates to a method for registering a portable unit with a specified fixed unit in a cordless telephone system, and in particular, to a method for transmitting ID numbers for portable and fixed units in a cordless telephone system by using both wire and wireless links.
2. Description of the Related Art
In order to register a portable unit with a specified fixed unit, a portable unit first transmits its own ID (identification) number to a fixed unit, and in response thereto, the fixed unit transmits its own ID number to the portable unit.
FIG. 1 is a diagram showing that a cordless telephone system transmits the ID numbers by using a wireless link according to the prior art. As illustrated, when transmitting the ID numbers by using a wireless link (labeled A), the cordless telephone system does not need additional circuitry. However, the portable unit does not know the ID number for the fixed unit with which its own ID number is to be registered. Thus, an unwanted fixed unit may respond to a request for the ID number from the portable unit and transmit its ID number to the portable unit. In order to prevent this, a user should depress a specified key provided on the fixed unit before registering the portable unit. In this case, a fixed unit whose specified key is not depressed by the user does not transmit its ID number to the portable unit, thereby preventing an erroneous registration of the portable unit with that particular fixed unit. However, in the case where a plurality of other fixed units are situated in the vicinity of the particular fixed unit, the user of the portable unit may need to repeatedly perform the above procedure in order to register the portable unit with a desired fixed unit. This results in a disadvantageous increase in the registering time. Besides, the portable unit may be erroneously registered with an unwanted fixed unit which is in the process of performing the registration procedure with other portable units, if any.
FIG. 2 is a diagram showing that a cordless telephone system transmits the ID numbers by using a wire link according to the prior art. As illustrated, when transmitting the ID numbers over the wire link (labeled B), the cordless telephone system may prevent the erroneous registration of the portable unit with the unwanted fixed unit, and reduce the registration time. However, the cordless telephone system needs an additional circuit for transmitting the ID numbers. In this case, the wire link commonly uses a charge terminal. However, by employing the charge terminal approach, a (+) terminal except for a (-) terminal must be connected to the two input/output terminals of the central processing unit (CPU), so that the CPU needs two additional terminals. That is, a bidirectional path must be implemented, as shown in FIG. 2, whereby both the portable unit and the fixed unit must be able to both drive and receive data over the wire link, thus, each requiring an additional terminal.